Heat exchanger tube



June 15, 1959 F, A. LoL-:BEL ETAL HEAT EXCHANGER TUBE Filed Feb. 21, 195e I INVENToRs: FREDERICK A REID EWING BY a f 1.a, l

. LOEBEL W ATr'xs HEAT EXCHANGE-R TUBE Frederick A. Loebel and Reid Ewing, Milwaukee, Wis., assignors to Cleaver-Brooks Company, a corporation `of Wisconsin Application February 2l, 1956, Serial N o. 566,797

2 Claims. (Cl. 13S-38) This invention relates to heat transferring apparatus and, more particularly, to tubes used in such apparatus.

The handling of many liquids requires heating in order to facilitate pumping and in other instances heating may be required to change the viscosity of the material for various applications. This is particularly true of liquid materials which are very viscous at ambient temperatures. Heat Vexchangers having tubes through which the material may be passed to receive heat are often used for this purpose.

In the operation of heat exchangers where a uid to be heated is passed through a plurality of heat exchanger tubes disposed in a heated chamber, a problem arises in evenly and thoroughly heating the more viscous fluids'.

This problem arises because viscous fluids generally move in laminar flow, rather than in turbulent ow. In laminar ilow, there are few eddy currents and no appreciable mixing ofthe various layers. As a result, the outer layers of fluid adjacent to the walls of the heat exchanger tube are heated or cooled to a greater degree than the inner layers. For this reason, the coeiiicient of heat transfer to the viscous fluids is generally lower than the coefficient of heat transfer from the fluids heating or cooling them. To overcome this problem it has been the practice in the past to provide internal heat conducting ns in the heat exchanger tubes.

Fins are used Where the heat transfer coefficient on one side of the tube wall is widely different from the heat transfer coefficient on the other side of the tube wall. The heat flow, of course, is limited by the side which has the greatest resistance, or the lowest heat transfer coefiicient. The use of fins is an attempt to overcome the effects of the poorer heat transfer coefcient by heating by conduction a greater amount of transfer surface.

The fins have been secured to the tube Walls in heat conductive contact, with portions extending inwardly of the tube to conduct the heat to the interior thereof, by relatively difficult and expensive operations, such as brazing.

An improved method of forming a heat exchanger tube havinginternal fins is disclosed in U, S. Letters Patent, No. 2,722,733, issued November 8, 1955, to Meyer and Loebel, wherein a plurality of inner tubes are disposed side by side within a heat exchanger tube in contact with each other and with the heat exchanger tube walls. In making the tube disclosed in said application, the diameter of the outer heat exchanger tube is reduced to Hatten portions of the inner tubes into heat conductive contact with the heat exchanger tube. This heat exchanger tube produces a very satisfactory result and is a simple, economical method of producing an internally nned heat exchanger tube.

it is desirable in such installations to attain maximum heat transfer coefficients by preventing too large a temperature difference being created between the inner and outer layers of iiuid. With installations having relatively short tubes there is adequate mixing of the -ud in the headers before such a temperature difference is created. With installations utilizing relatively long heat exchanger arentl` tubes, although there is adequate mixing of the fluid inthe headers, the problem lies in the fact that with such long tubes this large temperature dilerence is created before the fluid reaches the headers due to the combined effects of laminar ow and tube lengths. concerned primarily with the relatively long tubes and the means for obtaining mixing within the tubes and thus, maximum heat transfer coeicients.

Thegeneral object of this invention is to provide a newV and improved heat exchanger tube.

Another object of this invention is to provide a new and improved relatively long heat exchanger tube which is economical and relatively simple to produce and which provides efficient even heating of the more viscous fluids passed therethrough.

Another object of this invention is to provide a new and improved heat exchanger tube capable of providing adequate mixing within the tube of fluid passing therethrough so as to attain maximum heat transfer coefcients.

Afurther object of this invention is to provide a new and improved heat exchanger tube having at least two n sections angularly displaced relative to each other to provide mixing of the lluid within the tube.

AV more detailed object of this invention is to provide a new and improved heat exchanger tube having a cylindrical outer tube, iin sections disposed in series within the outer tube spaced longitudinally apart to provide a mixing chamber space within the tube, the `n sections' andmixing chamber space being arranged to thoroughly` mixthefluid as it passes through the tube.

Other objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a fragmentary side view, partially broken away, of a heat exchanger tube embodying the present invention;

Fig. 2 is a transverse, sectional view through the tube taken substantially along line 2 2 of Fig. l; and

Fig. 3 is a transverse, sectional view through the tube taken substantially along line 3-3 of Fig. l.

While the invention herein described is a preferred embodiment, it is not intended to limit the invention to the specific form and arrangement shown, it being contemplated that various changes may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Referring now to the drawings, there is shown a relatively long heat exchanger tube l which is adapted for use in a heat exchanger wherein a plurality of heat exchanger tubes. are disposed longitudinally and parallel to each other within an outer casing having a header or headers at each end. A fluid to be heated is pumped through the heat exchanger tubes so as to make a number of passages through the casing. The tubes may be heated by a heat transfer liquid continually passed through the casing in Contact with the outer surfaces of the heat exchanger tubes so that the heat is conducted from the transfer liquid through the walls of the heat exchanger tube l to the uid inside the heat exchanger tubes.

An embodiment of this invention is shown in Fig. l wherein the heat exchanger tube 1 includes a cylindrical outer tube 2 having a fm structure 3 disposed longitudinally therein. The n structure 3 comprises a first elongated iin section t disposed in one end portion of the outer tube 2 and a second elongated n section 5 disposed in the other end portion of the outer tube 2 in longitudinal series relation.

In more detail, the n sections 4 and 5 each comprise a plurality or set of inner tubes or iin-s 7 and 7', respectively, which are disposed side by side within the outer tube 2 with their axes parallel to the axis of the outer tube 2. Each set of tubes 7 and 7 are arranged so as to con- The present invention is 3 tact each other and the walls of the outer tube 2. In the embodiment of the invention shown in the drawings, the iin sections 4 and 5 each comprise three of the inner tubes 7 and 7', respectively, having their axes circumferentially disposed approximately 120 apart. To produce an efcient heat conductive contact between the tubes 7 and 7 and the outer tube 2, the method disclosed in the patent of Meyer and Loebel, No. 2,722,733, referred to above, is utilized wherein the cylindrical tubes 7 and 7 are positioned, as above described, within the outer tube 2 and the diameter of the outer tube 2 is reduced by a swedging operation wherein the inner tubes are flattened adjacent the outer tube 2 to provide the metal to metal heat conductive contact. With this construction heat is conducted from the wall of the outer tube 2 to the walls of the inner tubes 7 and 7 to more eiciently heat the fluid passing through the heat exchanger tube 1.

As shown in Figs. 2 and 3, a plurality of walls 8 andV 8' of the inner tubes 7 and 7 dene a plurality of separate spaces or passages 9 and 9 within the outer tube 2 for the flow of uid therethrough. In each of these passages 9 and 9', especially in the relatively long heat exchanger tubes with the more viscous fluids flowing in laminar ow, the layer of uid adjacent to the inner tube walls 8 and 8' is heated to a greater degree than the layers of uid nearest the center of the tubes 7 and 7. It has been found that this effect may be substantially compensated for by angularly displacing the two n sections 4 and 5 circumferentially with respect to each other. In the embodiment of the invention shown in Figs. 2 and 3, it may be seen that the iin sections 4 and 5 have been angularly displaced approximately 60. Comparing Figs. 2 and 3 it is evident the wall portions 8 of the tubes 7 in the downstream iin section 4 are in longitudinal alignment with the spaces or passages 9 defined by the wall portions 8 of the tubes 7 in the upstream n section 5. By thus offsetting the two iin sections 4 and 5, the body or slug of fluid passing through each passage 9 of the upstream n section would impinge upon the wall portions 8 of the tubes 7 in the downstream iin section 4, a cool layer of iiuid from the center of each passage 9' thus entering one of the passages 9 in a better heat transfer position adjacent the tube walls 8. There is, thus provided, a mixing of the uid passing between the two n sections 4 and 5 within the outer tube 2 and a better heat transfer to the fluid passing therethrough.

Additional and more complete mixing of the uid may be achieved by providing a mixing chamber space 6 approximately at the midpoint of the outer tube 2. The mixing chamber space 6 shown in Fig. l which is free of any fin section is formed or defined by longitudinally spacing apart the 1in sections 4 and 5 intermediate the ends of the outer tube 2. A spacer member or rod 10, best shown in Fig. l, is disposed in the mixing chamber space 6 and is secured at each end to the 1in sections 4 and 5 adjacent the inner contacting portions of the tubes 7 and 7', respectivley. The spacer member 10 is secured to the two iin sections 4 and 5 to form the substantially rigid iin structure 3 which is inserted as a unit within the outer tube member 2. The spacer member 10 acts to hold the two 1in sections 4 and 5 together in predetermined longitudinally spaced and angularly displaced relations during assembly thereof and during the swedging operation.

To provide turbulence and more thorough mixing of the iluid passing through the mixing chamber space 6, baffles may be disposed therein. In Fig. 1, a single an nular radially extending baflle 11 is secured to the spacer rod 10 intermediate its ends. In the embodiment of Fig. 1, the baffle plate 11 is secured somewhat closer to the upstream iin section 5 of the heat exchanger tube 1 than to the downstream n section 4.

It is to be understood that with extremely long heat exchanger tubes and with particularly viscous uids that it may be advisable to use more than two angularly displaced fin sections to provide the desired heat transfer and that, therefore, a plurality of mixing chamber spaces and angularly displaced n sections may be provided in a particular installation without exceeding the scope of the invention, as claimed.

We claim:

1. A heat exchanger tube comprising; a relatively long cylindrical outer tube, a pair of tubular fin sections disposed longitudinally in series relation within said outer tube, each of said iin sections including a plurality of inner tubes having their axes parallel to the axis of the outer tube and having pressed metal to metal contact with the outer tube for heat conduction to the interior thereof, said pair of n sections being spaced apart longitudinally in the outer tube to form a mixing chamber space within the outer tube between the iin sections, said iin sections being angularly displaced with respect to each other and having tube walls of one section in alignment with passages through the tubes of the other section to divide the ows from each tube of the upstream section and thereby maintain good heat transfer to fluid in the outer tube, and a rod within the mixing chamber space having opposite ends rigidly secured respectively to the two tin sections to hold the sections in the defined longitudinally spaced and angularly displaced positions relative to each other.

2. A heat exchanger tube as dened in claim 1 including a radially extending disc-like baie plate of less diameter than said outer tube secured to said rod intermediate its ends to promote turbulent fluid ow through the mixing chamber space.

References Cited in the file of this patent UNITED STATES PATENTS 1,283,550 Parker Nov. 5, 1918 2,034,822 Morrow Mar. 24, 1936 2,230,221 Fitch Feb. 4, 1941 2,722,733 Meyer et al. Nov. 8, 1955 FOREIGN PATENTS 3,994 Great Britain of 1875 321,168 Great Britain Oct. 31, 1929 449,046 Great Britain June 19, 1936 

